Abstract: The sedimentary sequence of the Bayan Har basin indicates that the formation to elimination of the basin was a process of continuous deposition and tectonic evolution. The basin was rifted and pulled apart on the basis of the Early Paleozoic passive continental-margin shallow sea and ran through in the Devonian; the ocean basin expanded into a mature open ocean in the Early Carbonaceous; its northern part began consumption and its southern part continued expansion in the Late Carboniferous; the oceanic basin changed into a remnant ocean in the Late Permian to Middle Triassic and into a peripheral foreland basin in the Late Triassic; and it completely closed at the end of the Triassic. Its main part is composed of Early-Mid Triassic abyssal sediments and typical flysch and Late Triassic neritic flysch, tempestite and marine molasse. In its northern part Middle Permian seamount sediments are exposed and north of the Kunnan junction zone there occur Early-Mid Triassic island-arc deposits. Centering on the basin, the blocks on the northern and southern sides were subducted in opposite directions and collisional orogeny at the eastern and western ends of the basin occurred not later than the Late Permian. All these features suggest the nature of a Late Permian-Middle Triassic remnant basin for the Paleo-Tethys and the position of the main ocean domain.